In bicycle gear systems it has long been known and common to equip a rear derailleur with two jockey or guide wheels or chain guide rollers that are rotatably borne in a pre-tensioned chain guide arrangement. These guide wheels have a plurality of functions. They tension the return path of the chain and provide sufficient chain length corresponding to the selected gear ratio of the chain gear system. Moreover, in the chain guide arrangement it is the task of the guide wheels to reliably guide the chain, even when there is strong axial displacement or the chain is on an incline, as may often happen during gear changing.
A number of rear derailleur devices are known from the prior art. For instance, DE 296 23 610 U1 provides a rear derailleur for a derailleur gear system that has guide wheels of different sizes.
DE 1 262 141 illustrates a guide wheel with partly or completely beveled profile surfaces along the gear teeth. What this achieves during operation is that individual teeth in the gear teeth can engage more easily in the intermediate spaces in the chain.
U.S. Pat. No. 4,575,365 illustrates a derailleur with guide wheels that are embodied with greater material thickness in their bearing area in the clearly radial distance from the tooth gap base about the central opening for improving the bearing properties. This measure has no effect on guiding the chain because the thickening in the guide wheels in the radially inner area does not interact with the chain supported on the guide wheel. A similar solution is known from U.S. Pat. No. 5,711,731.
As is generally known, depending on the type of construction, conventional bicycle chains have alternating outer and inner chain links that connect successive chain rollers to one another. Corresponding alternating link spacing results from the alternating arrangement of outer and inner chain links, i.e. smaller link spacing is present between the inner links and relatively larger link spacing is present between the outer links. When the outer gear teeth are embodied with an essentially constant thickness for all of the teeth, as is the case with the solutions from the prior art described in the foregoing, all of the teeth must be matched to the smaller link spacing between the inner chain links so that the teeth between outer chain links engage with substantial lateral clearance. However, this is at the expense of the guiding properties of the gear teeth, because the chain is guided laterally (axially) only by every second set of links, specifically always by only the inner chain links and their smaller link spacing that is matched to the tooth width. This can lead to problems, especially when the chain is subjected to strong inclines in certain gearing positions or during gear changing. In certain riding situations this can result in strong vibrations that may lead to the chain slipping completely off of the guide wheel. In addition, other consequences of this problem may be gear changing problems, the chain jamming, noisiness, and increased wear. The limited guiding properties of conventional chain guide arrangements may lead to problems, especially in new derailleur gears that have a plurality of sprockets on the rear axis of the bicycle.
U.S. Pat. No. 4,174,642 describes a chain drive sprocket for agricultural machinery such as conveyor mechanisms, the outer teeth of which alternate in thickness. The teeth are provided with angled faces that function to center the chain on the sprocket.
An underlying object of the invention is to provide a guide wheel and a derailleur embodied therewith that has improved guiding properties.